You don't need to drain the tank, but you will need to clamp or plug the fuel line(s).

The previous poster mentioned an access problem. Fuel pump work on cars that have a rear-mounted pump is more easily achived if you first back the car up on ramps. You don't have to back up all the way, but enough to give you added crawling space. Afterwards, set the parking brake and block the front wheels. I always pull the ground strap off the battery too. If you create a spark by unintentionnally grounding something, you and the car may be unintentionally gone.